1. Field of the Invention
The present invention relates to a method for wireless data communication between a base station and at least one transponder by a high-frequency electromagnetic carrier signal, onto which information packets are modulated. Each information packet has a header section, a middle section, and a terminating end section, wherein the middle section has a data field containing the data necessary for the data communication.
2. Description of the Background Art
The invention falls within the realm of transponder technology and in particular within the field of contactless communication for the purpose of identification. Although it can be used in principle in any communication systems, the present invention and its underlying problem are explained below with reference to so-called RFID communication systems and their application. Here RFID stands for “radio frequency identification.” Reference is made on the general background of this RFID technology to the “RFID-Handbuch” (RFID Handbook) of Klaus Finkenzeller, Hanser Verlag, third updated edition, 2002, which is also published in English by John Wile & Sons.
In the case of transponders, an electromagnetic signal transmitted by the base station is received and demodulated by the transponder. Active, semipassive, and passive transponders are differentiated here depending on the design of their energy supply. In contrast to active transponders, passive transponders do not have their own energy supply, so that the energy necessary in the transponder for demodulating and decoding the received electromagnetic signal must be obtained from this electromagnetic signal itself transmitted by the base station. In addition to this unidirectional energy transfer, bidirectional data communication as well typically occurs between the base station and transponder.
The basis for the bidirectional data transmission between the base station and transponder forms a communication protocol, which specifies, in addition to the data information to be transmitted, control information for the data communication.
A generic RFID communication protocol for a known data communication between a base station and transponder is described in the Unexamined German Patent Application DE 101 38 217 A1, which corresponds to U.S. Publication No. 20030133435. Accordingly, an information packet to be transmitted from the base station to a transponder has at least one header section, a middle section, and an end section. The header section defines the number of data to be transmitted and their identification. The middle section contains the data to be transmitted in each case. The end of the information packet is communicated in the end section to the receiver of the data transmitted in each case. The data communication is protected with protection mechanisms, such as, for example, a CRC protection field or parity bits.
A generic RFID method and system for bidirectional data communication is also the subject of the so-called Palomar Project, which was established by the European Commission as part of the so-called IST program. With respect to the content of the Palomar project, reference is made to the related, generally available publication of the European Commission of Jan. 11, 2002, which corresponds substantially to the ISO standard 18000-6.
For further background on bidirectional data communication between a base station and transponder, reference is made further to the Unexamined German Patent Applications DE 102 04 317 A1, DE 100 50 878 A1 (which corresponds to U.S. Publication No. 2002044595), and DE 102 04 346 A1, and the European patent EP 473 569 B1 (which corresponds to U.S. Pat. No. 5,345,231).
In most UHF- and microwave-based RFID systems and/or sensor systems, the data communication between the base station and transponder is initiated first by the base station with the base station transmitting a request signal (command, data request) to the various transponders located within the vicinity of the base station. The transponder(s) participating in the data communication typically respond(s) to this request with a response signal (response), but only if the transponder(s) has (have) received a complete and valid command from the base station. The transponder can now be operated synchronously or asynchronously relative to the base station.
Data communication between the transponder and the base station occurs only after a complete and valid command has been received. If, however, a transponder receives no valid command it sends an error code back to the base station to signal thereby that it has not received a valid command. The transponder, for example, does not receive a valid command if the communication line between the base station and the transponder was disrupted, for example, by overlapping of interfering signals so that the transmission of the command could not be entirely concluded. Another source of error is, for example, faulty demodulation and decoding within the transponder.
In addition, it may also be the case that the transponder is not even designed for decoding commands from the transmitting base station, for example, because of its construction. This transponder would then transmit an error code continuously back to the base station even if there is a trouble-free communication line. The base station, which is now incapable of differentiating whether an error code was transmitted due to a faulty data communication or originated from a transponder not designed for data communication with the base station, would then attempt continually to create a data communication with this transponder, although this is technically impossible. Particularly if the base station would like to communicate with very many transponders, this ties up very many resources of the base station, which can lead very easily to jams in the data communication.
A similar problem arises when the base station has already established data communication with one or more transponders and during the course of this data communication at least one other transponder would like to participate therein, without the base station receiving information on the presence of this additional transponder. These later joining transponders, which are not yet synchronous with the already existing data communication, as a result send constant error codes, which must be processed by the base station. This ties up additional resources of the base station, which can lead very rapidly to jams in data communication particularly in the case of very many additionally joining transponders. On the one hand, there is indeed the need to establish a functioning data communication with all possible transponders that can be accessed by the base station. On the other hand, however, such communication jams between base stations and transponders are to be prevented as much as possible to maintain a high performance of the data communication system.
Existing RFID systems differ in particular through the use of different transponders; in this case, the differences of the different transponder derive substantially from their different function. Transponders differ from each other in particular in the commands and the number of commands they support, i.e., that they can demodulate and decode. In particular, so-called low cost transponders have a limited instruction set, which is hard-wired, for example, or placed in a separate instruction memory specifically provided for this purpose. The functionality of a transponder increases with an increase in the instructions in its instruction set. The increase in functionality, however, goes hand in hand with an increase in transponder circuit costs and thereby an increase in price. For this reason, transponders are equipped with a specified instruction set with a specified size, depending on their intended application. However, it is problematic in this case that this rigidly predetermines the functionality, which leads to a rather limited transponder flexibility.
To realize an increase in flexibility and thereby in the functionality of a transponder, a transponder would have to be provided with very different instruction sets and thereby with many instructions to be able to communicate with very different base stations. This in fact makes it possible to control individually at least the transmission times between the base station and the transponder for the specific commands. Nevertheless, a very large number of commands would have to be provided here, which would have to be stored in a memory specifically provided for this in the transponder or alternatively hard-wired into the transponder. The associated increase in chip surface area of the transponder is also reflected in its higher cost.